The entire disclosure of Japanese Patent Application No. 2010-280188, filed Dec. 16, 2010 is expressly incorporated by reference herein.
1. Technical Field
The present invention relates to an optical position detection device that optically detects a position of a target object and an apparatus with a position detection function including the optical position detection device.
2. Related Art
As an optical position detection device that optically detects a target object, for example, a device in which detection light is output from respective plural detection light sources via a light-transmissive member toward the target object and the detection light reflected by the target object is transmitted through the light-transmissive member and detected in a light receiving unit has been suggested. In the optical position detection device having the configuration, the position of the target object is detected based on the detection result of the detection light in the light receiving unit. See Japanese Patent Publication No.
Further, a system in which a light-guiding plate is provided in an optical position detection device and detection light output from respective detection light sources is output via the light guiding plate toward a target object and the detection light reflected by the target object is detected in a light receiving unit has been proposed. See Japanese Laid-Open Publication numbers JP-A-2010-127671 and JP-A-2009-295318.
When the optical position detection devices disclosed in the above Japanese publication documents are actually used, detection light reflected by an object other than the target object in addition to the detection light reflected by the target object enter the light receiving unit. Therefore, there is a problem that position detection accuracy of the target object is low. For example, in the optical position detection device disclosed in JP-T-2003-534554, detection light reflected on the rear surface side of the light-transmissive member enter the light receiving unit. Further, in the optical position detection devices disclosed in JP-A-2010-127671 and JP-A-2009-127671, when an object other than the target object such as an accessory exists in the output space of the detection light, the detection light reflected by the object enter the light receiving unit.
Note that, in the case in which ambient light such as outdoor light enters the light receiving unit in addition to the detection light reflected by the target object and the detection light reflected by the other object than the target object, the influence of the ambient light may be eliminated relatively easily unlike the influence of the detection light reflected by the other object than the target object. For example, in the case in which pulse-modulated light is used as detection light, because received light signals of the detection light reflected by the target object are high-frequency signals and received light signals of ambient light are low-frequency signals, the received light signals corresponding to the ambient light may be eliminated relatively easily using a high-pass filter. Furthermore, if the position of the target object is detected using a drive condition for the detection light sources when the detection light sources are differentially driven so that detection intensity may be equal in the light receiving unit, the influence of ambient light may be eliminated. Note that, in these methods, it is impossible to eliminate the influence of the detection light reflected by the other object than the target object.